So, I ordered the same AFR gauge I used to tune the DIY supercharger conversion I designed for the A-Series engine, which worked very well. It'll get here Wednesday.

I also ordered a short exhaust adapter that will let me weld in a bung for the O2 sensor, and place it between the 18" head pipe from the rear cylinder and its muffler. Easy peasy to wire in the gauge (the broadband sensor is heated, so it needs power, too).

I hope to have the setup installed next weekend, and will post the data from the trials. The resulting data should be useful to people at my altitude (5,000 to 6,000 ft.) running the S&S Super E with internally stock 74" engines and dual pipes, at least as a starting place.

 

Bent up a little temporary mount for the AFR gauge which bolts to the GoPro mount from some aluminum bar I had lying about, so I can see it while driving (see pic).

These are the AFR targets I provide to people tuning my blow-through supercharger setup for the A-Series:

• Light throttle - 14.5:1 ~ 14.7:1 (stoichiometric is 14.7:1)
  
• Heavy throttle/Boost - 11.8:1 ~ 12.5:1
  
• Cruising (level ground) - 15:1 ~ 16:1
  

The hard acceleration/boost target is a bit rich for a naturally aspirated engine. That said, the A-Series likes to run a bit rich, even naturally aspirated, due to 'charge robbing' resulting from siamese intake ports--one for no. 1 & 2, the other for no. 3 & 4--and the engine's valve timing. Does anyone know what a Shovelhead typically likes to run at? Does a Harley suffer from any charge robbing due to the siamese intake port and the engine's valve timing?

 

Two things about these Gasbox reproduction Sportster mufflers.


First, I was talking to Gasbox this morning, and the baffle I showed earlier--a ring about halfway down the perforated interior pipe--was a disc in the stock Harley muffler back then. So, 100% of the exhaust gasses were directed through the perforations, out through the outer chamber, then again through the remaining perforations and out the pipe. Gasbox bores a hole in the center to improve the flow slightly--but of course also increasing the noise a bit.

Second, it turns out that Gasbox makes a 22" version of these mufflers, which evidently is used in stock Sportster application for a 2 into 1 system. The 22" mufflers would extend right to the rear edge of my tire. I'm not sure whether I'd like that aesthetic but when they finish the batch they're making, I'm going to order one so I can hold it up and see how it would look. I wouldn't mind a skosh more noise suppression if the look isn't too clunky...

 

Update on the last post: I was wrong, and the longer 2 into 1 Gasbox muffler is too fat to work with these pipes. Anyway, I now like the way this system sounds and have decided to leave it as is. A guy was cruising beside me with drag pipes the other day, and these are significantly quieter. Also, I like the idea of using vintage Sporty mufflers on a Pan-Shovel bobber.

Money-saver: I found the source of the mysterious miss, which was a very small air leak into the S&S manifold at the head. The PO had combined O-rings and rubber bands together, and in my ignorance of this year of Shovel heads, I followed suit. Removed the rubber bands, installed smaller I.D. clamps, and voila. Silky smooth idle and zero miss. I hope to find time soon to finish fitting the AFR gauge, and I'll bet my difficulty dialing in the mixture will vanish, too. I'll be shooting for jets that give me a decent AFR from below 4,000 ft. to as high as ~9,000 ft., if that's possible with this Super E carb.

Anyway, you can get good quality 3/4" wide stainless, floating bridge, curved T-bolt clamps from Scamazon for less than half of what S&S wants for their clamps. See pics.

 

[QUOTE=NM Pan-shovel;20654251] I'll be shooting for jets that give me a decent AFR from below 4,000 ft. to as high as ~9,000 ft., if that's possible with this Super E carb.

Simple carbs are an inherent compromise on fuel mixture alone, add in altitude changes and you exacerbate the situation.
I`m sure you`ll get it to work ( plenty smart dude) and lots of folks love an S&S carb
Starting with a CV 40 would at least minimize the altitude problem.

Great build ! Hat`s off to you !

 

[QUOTE=eighteight;20654396]Thanks for the kind words!

I've thought about a CV carb re: the altitude issue, especially if I want to ride cross-country. No loyalty to the Super E; that's just what was on it, and of course is straightforward to re-jet. I do have experience with the SU CVs, which use an oil-dampened, spring-loaded aluminum slide and vacuum chamber rather than a rubber diaphragm, and was surprised to read that some people have adapted a model very similar to the HIF44 used in my DIY blow-through supercharger conversion for the British A-Series engine.

The 40mm CVs seem to be far cheaper than the 1-3/4" SU (which works better than the 1-5/8" version on the 1275cc A-Series), but I have zero experience with them. Are they difficult to tune? I assume you're suggesting a post-'89 version with an accelerator pump...? How do these compare with the Mikuni? The '38 flathead I bought back in the late '70s had a Mikuni on it (if I'm remembering correctly), but then I only rode it at sea level in San Diego.

 

For those elevations I would think a .028"/.068" should be close... But the nice thing I hear about the CV carb is that it will compensate on its own for elevation changes..

 

Yes I remember when Rivera Eng. sold the Skinners Union set up for H-D`s I had them on an MGB " Top off the dash pots Nigel !
Mikuni has many adherents, claim "snappier" response due to no lag from vac chamber
The CV ( yes to the later version )is simple to tune and will support 100HP
Parts are readily available

 

While there seems to a bunch of extolling of the CV carb's ability to handle changes in elevation, it's not as good as some think. I've run both a Super G and CV51 on a bike from 200 feet below sea level to 6600 feet with a wide band afr sniffer. In both cases the motors picked up about the same richness based on the gauge. Both idle up to about 1/8 throttle and WOT function the same on the 2 carbs. The big issue on butterfly only carbs (SnS super) is the crossover between low speed and high speed jetting. The SnS carb cam have quite a bit of fluctuation of AFR on the transition. The CV (or slide/needle) car will not. The fluctuation becomes exacerbated with altitude at times enough to cause a hesitation.

I would guess that you could try installing an adjustable air bleed to help with the transition like on the Tjet kit.. They are external and easy to change..

 

Thanks, gents. When time permits, I'll certainly report back with which jet combo nets appropriate AFR readings at my daily cruise range of 5,000 to 6,000 ft.

Yes - I think CVs do compensate to some extent, but ultimately the needle profile sets the outer limits (at least it does in the SU case).

Okay, good to know the commonly available CV40mm is easy to tune. That certainly seems like the 'go to' option, as the SU carbs are expensive and manifolds rare (I'd probably end up machining an adapter if I went that route).

Max, thanks for the additional info on CVs vs. butterfly-style S&S. That is a consideration, and I read the (scanty) installation and tuning instructions with some hesitation; they say virtually nothing about how to use the air bleed jet circuit. But it's really useful to know that in your experience the designs aren't terribly different--but for the jet crossover issue. That may be the deciding factor, given that I do plan on some interstate rides and live at relatively high altitude.

Just for the sake of conversation what about this dual 30mm Mikuni setup? (I'm talking about kit#2 with the low-profile air cleaners). Nice-looking manifold, but seems like it might net a knee position even more skewed than the S&S Super E's standard air cleaner. I'd like to email the guy to ask him for an actual measurement from rocker cover to outer edge of air cleaners.

You might think a combined 60mm of throat is a lot for a 1200cc engine, but the 1275cc A-series came from the factory with twin 1.25" or 31.75mm SUs. They provide decent torque but very good throttle response and a respectable top end.